NICU Conversions and Calculations

Patients monitor in neonatal ICU

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Medical professionals use many calculations every day to keep babies healthy and strong in the neonatal intensive care unit (NICU). Although you don't have to know how to do this math when your baby is in the NICU—the healthcare providers will manage these calculations for your baby—many parents or caregivers like to know anyway. If you want to give it a try, grab your calculator and start crunching some numbers.

Basic Measurement Units

Nurses in the NICU talk a lot about fluid volumes and a lot about weights. Here's one simple fact every parent or caregiver will learn early on the journey: 1 milliliter (ml) = 1 cubic center (cc) = 1 gram (g). Milliliter, cubic center, and gram are essentially interchangeable.

When you hear one nurse say, "Your baby is eating 25ml" and another one says, "Your baby took 25cc from the bottle," they are talking about equal amounts.

Volume vs. Weight

Note that cc and ml are measures of volume and grams are a measure of weight. One cc (or ml) = 1 gm only for water at 4 degrees C. But since many measurements in the NICU (formula, IV fluids, body fluids) are mostly water, the two are considered essentially equal.

Another quick and easy one to know is that 1 kilogram (kg) is the same as 1,000 grams. So a 2.3-kilo baby weighs 2.300 grams (2.3 x 1,000). Some more basic weights and measures that help put things in perspective:

  • 5 grams = 1.18 teaspoon (tsp)
  • 15 grams = 3.6 tsp (or 1.2 tablespoon)
  • 30 ml = 1 ounce

Weight Conversions

Most hospitals use the metric system, so it's helpful to know how to convert from metric measurements to the Imperial system (pounds and ounces). 

  • 1 kilogram = 2.2 pounds
  • 1 pound = 0.45 kilograms

If your preemie weighs 2.8 kilograms,

To get your baby's weight in pounds (lbs), you’d multiply their weight in kilograms by 2.2. So, if your baby weighs 2.8 kilograms, that calculation would look like this: 2.8 kg x 2.2 = 6.16 lbs.

To make the calculation in the other direction from pounds to kilograms, you'd multiply your baby's weight in pounds by 0.45. So if your preemie weighs 1.8 pounds, the calculation would look like this: 1.8 lbs x 0.45 = 0.81 kg. (If you multiply this kilogram weight by 1,000, you have the weight in grams. In this case, 0.81 kilograms is 810 grams.)

Nutrition Calculations

Healthcare providers and dietitians calculate how many calories your baby needs every day. Whether the calories come from IV fluids, breast milk, or formula, they’re always based on your baby's weight, so the amounts change frequently as your baby grows.

Of course, each baby is unique and each healthcare provider has a different approach to calorie management. Typically, babies need 100 to 150 calories per kilogram of weight each day. (Every baby is different, so ask your NICU staff to better understand what calculations they are using).

For example, if your baby weighs 3.4 kilograms and providers want the baby to have 120 calories per day per kilogram, you'd multiply 3.4 kg x 120 to get a goal of 408 calories per day.

Typically, breast milk and standard formula have 20 calories in every ounce. If your baby is fed every three hours, that equals eight feedings each day. Divide those 408 daily calories into eight feedings and you get 51 calories per feeding.

Then divide the number of calories for each feeding by 20 to figure out how many ounces of milk your baby needs. In this example, 51 calories divided by 20 calories per ounce equals 2.55 ounces. Since there are 30 ml in every ounce, 2.55 ounces is the same as 76.5 ml.

Fortifier Calculations

For a small baby, 76.5 ml is a big feeding, and a baby’s stomach may not be able to handle so much volume. Most NICUs add calories to breast milk or formula with powdered, liquid, or Prolacta fortifiers so that there are more calories in every ounce. Rather than 20 calories per ounce, fortifier can make it 22 calories per ounce—or 24 calories, 26 calories, and even higher if needed.

If your baby's milk is being fortified to 24 calories per ounce, they need only 2.1 ounces, or 63 ml, of milk at every feeding. If their milk is fortified to 28 calories per ounce, they need only 1.8 ounces, or 54 ml, of milk per feeding (51 ÷ 28 = 1.8).

Temperature Calculations

Normal body temperature for a baby is 37.0 degrees Celsius, or 98.6 degrees Fahrenheit. It's the same for preemie babies and full-term babies alike. It's pretty easy to use an online tool to convert Fahrenheit to Celsius or vice versa. But if you want to do it yourself, here's how.

If you have a temperature in Fahrenheit and you want it in Celsius, subtract 32 from the temperature in Fahrenheit, and then multiply by 5/9.

(Temp[F] - 32) x 5/9 = Temp[C] 

If the temp is 99.2 in Fahrenheit:

99.2 - 32= 67.2. Then, 67.2 x 5/9 = 37.3

99.2 F = 37.3 C

You can reverse this if you have the temperature in Celsius and want to know Fahrenheit (and this is more common since parents in the U.S. are used to Fahrenheit and healthcare providers often use Celsius).

(Temp[C] x 9/5) + 32 = Temp[F]

If the temp is 38.1 Celsius:

38.1 x 9/5 = 68.6. Then, 68.6 + 32 = 100.6

38.1 Celsius = 100.6 F (This is a fever for a newborn.)

A Word From Verywell

These basic, frequently used NICU conversions and calculations are relatively simple to do. Plus, having a better understanding of terminology and procedures can help you feel more empowered while your baby is in the NICU.

By Trish Ringley, RN
Trish Ringley, RN, has been a NICU nurse since 1997 and owns Every Tiny Thing, an online store serving preemies and NICU families.